Few things in medicine are linear. DNA has error-correcting codes, much like a hard drive or network connection.

In hard drives or networks, errors are tolerable below a certain threshold. It's a different story once unrecoverable errors start to occur (data loss, system crashes, perhaps errors getting caught by higher-level things like exceptions).

I'd expect DNA, cells and biological systems are probably similar. The error correcting mechanisms can probably handle some errors up to a threshold (which probably itself varies between individuals).